The field of the disclosure relates generally to a blade or bucket for use in a rotary machine, and more particularly to a part-span shroud for stabilizing such blades.
At least some known rotary machines, such as steam turbines or gas turbines, include a fluid flow path generally defined between a stationary component and a rotating component. Such known rotary machines may include stationary vanes and rotating blades arranged in alternating rows so that a row of vanes and an immediately downstream row of blades cooperate to form a “stage.” Each stage may include a number of stationary vanes coupled to the stationary component in a circumferential array, extending radially inward into the fluid flow path, and a number of rotating blades coupled to the rotating component in a circumferential array and extending radially outward into the fluid flow path. The vanes are oriented to direct fluid flow at a desired angle into a row of blades immediately downstream. Known blades include airfoils that extract energy from the fluid, thereby developing the power necessary to drive the rotating component and an attached load, for example, an electrical generator or a pump.
In at least some known rotary machines, the rotational speed of the rotating component may induce an undesirable amount of vibration and/or axial torsion into low-pressure stages of the rotary machine, for example. To limit such vibration and/or axial torsion, at least some known blades include part-span shrouds extending from the airfoils at an intermediate radial distance between a tip and a root section of each blade. The part-span shrouds are typically coupled to each of the pressure (concave) and suction (convex) sides of each blade airfoil, such that during operation of the rotary machine, circumferentially adjacent part-span shrouds on adjacent blades contact each other during rotation of the rotating component.
Typically, part-span shrouds are coupled to the suction side of each blade and to the pressure side of each adjacent blade such that the leading and trailing edges of the part-span shrouds are substantially parallel to the direction of rotation of the blades. In other words, if adjacent blades are viewed along a radial direction, from above the blade tips and toward the blade roots, the part-span shroud leading edges all lie approximately on a straight line, and the part-span shroud trailing edges all lie approximately on a straight line. In such an orientation, a trailing edge portion of such symmetric part-span shrouds may extend at least partially within the throat of the flow path between adjacent blades. That is, the shrouds may extend into the location of minimal cross-sectional flow path area between adjacent blades and cause a loss of efficiency in the extraction of work from the fluid. In addition, because it would be undesirable to extend the part-span shrouds further into the throat area, such aligned part-span shrouds can provide relatively little structural support to the trailing edges of each blade.
At least some known blades have attempted to overcome these drawbacks by coupling the part-span shroud such that its leading edge extends from the leading edge of the suction side of the blade to an intermediate location along a chord of the pressure side of the adjacent blade. In such an orientation, the part-span shrouds are not aligned in the direction of rotation. This orientation facilitates moving the trailing edge of the part-span shrouds from the throat area, while providing support to the trailing edge of the blade. However, locating the leading edge of the part-span shroud at the leading edge of the suction side of the blade may produce an undesirable degree of obstruction of the flow at the blade leading edge, resulting in a decreased efficiency.